As increases in the clock frequencies of CPUs have made it possible to process large amounts of data, problems such as noise resulting from increases in signal transmission speed and crosstalk between signal lines have become serious, so that the limits of high-speed transmission through a metal interconnection line using a CPU have started to appear. Therefore, vigorous studies have been made of optical data communications as means for transmitting large amounts of data.
In the case of using light in data communications, it is possible not only to achieve high speed but also to solve the problem of crosstalk between interconnections because of the characteristics of optical data communications. Therefore, in the case of long-distance signal transmission, optical communications using optical fibers have been commonly used. Optical communications are also effective in the case of signal transmission of an extremely short distance as between boards or circuits. Studies have been made of a polymeric optical waveguide because of its compatibility with a printed wiring board (PWB) for the case of applying optical communications in signal transmission of an extremely short distance as between boards or circuits.
The polymeric optical waveguide used in optical interconnections is a relatively large multi-mode waveguide of approximately 50 μm in core diameter because of short transmission distance. The key to its realization is how easily it can be connected to light-receiving and light-emitting elements.
There are proposed optical waveguides in which a mirror disposed at an angle to a core, and a lens formed of the same member as a cladding or the core and focusing light onto the mirror, are provided in order to facilitate alignment of the optical axes of a module and the waveguide (see Patent Documents 1, 2, and 3).
[Patent Document 1] Japanese Laid-Open Patent Application No. 2001-166167
[Patent Document 2] Japanese Laid-Open Patent Application No. 2001-281486
[Patent Document 3] Japanese Laid-Open Patent Application No. 2004-361858